Apparatus for detecting the rotor position of an electric motor and related method

ABSTRACT

An apparatus for detecting a position of a rotor of a DC motor with N phases having a plurality of windings. The apparatus includes circuitry to couple at least two of the windings between a supply voltage and a reference voltage according to a first current path and allow the current stored in the two windings to be discharged through a second current path. The circuitry is configured to force the at least two windings at a short circuit condition in the second current path. The apparatus also includes a measurement circuit configured to measure the time period of discharging the current stored in the two windings and a rotor position detector for detecting the rotor position based on the measured time period.

FIELD OF THE INVENTION

The present disclosure relates to an apparatus for detecting a rotorposition of an electric motor, particularly of a brushless motor, and toa related method.

BACKGROUND

The identification procedure for identifying the position of a rotor ina sensorless brushless DC motor (BLDC), normally called “inductivesense”, takes advantage of the different response of the current in themotor winding with respect to a voltage pulse applied to the ends of thewindings of the motor itself. The knowledge of the rotor positionpermits optimizing the motor startup procedure and is therefore a veryimportant factor. The procedures of identifying the rotor positionshould therefore be characterized by high performances in terms ofprecision and insensitivity to disturbances.

Indeed an error in detecting the rotor position may result in animprecise excitation sequence of the stator phases and in a consequentefficiency reduction or, in the worst case, in a failure of the motorstart-up procedure (loss of synchronism).

The previous methods of detecting the rotor position (inductive sense)may only ensure good performance under conditions of unchanging supplyvoltage and precise current measurement.

The methods commonly used for detecting the position of the rotor, socalled inductive sense methods, are based on the analysis of the currentin the windings based upon a current pulse applied to the windingsthemselves. The different responses to the current pulses are based onthe magnetic saturation level of the windings, which is a function ofthe position of the rotor position. In this way, the magnetic saturationlevel allows detection of the rotor position.

EP 1309078 discloses a method for detecting the position of a rotor of aDC motor with N phases having a plurality of windings. The methodincludes the steps of coupling at least two of the windings between thesupply voltage and ground according to a first current path for aprefixed time (Tact), allowing the current stored in the two windings todischarge through a second current path, comparing the voltage at theends of one of the two windings with a prefixed voltage and providing acontrol signal when the voltage is smaller in absolute value than theprefixed voltage. The method also includes performing the above stepsfor each of the windings of the DC motor and detecting the position ofthe rotor based on the control signals obtained.

This method is sensitive to the power supply variation because thecurrent discharge is obtained by forcing the power stage at the highimpedance condition, and the current charge is obtained by coupling thewindings between the power supply and ground (current peak is functionof the power supply).

US 2012/0098474 discloses an apparatus for detecting a position of arotor of an electric motor having three phases and a plurality ofwindings. The apparatus includes circuitry to couple at least two of thewindings between a supply voltage and ground according to a firstcurrent path, disconnect the at least two windings and allow the currentstored in the two windings to be discharged through a second currentpath. The apparatus includes a measurement circuit adapted to measurethe time period between the start instant of storing the current in thetwo windings and the final instant of discharging the current in the twowindings, and a rotor detector for detecting the rotor position based atleast in part on the measured time period.

Even this apparatus is sensitive to the power supply variation becausethe current discharge is obtained by forcing the power stage at the highimpedance condition and the current charge is obtained by coupling thewindings between the power supply and ground.

Also, apparatus for detecting the position of a rotor of a DC motor areknown which use one sense element for each motor winding. The senseelements are embedded and coupled to the low side (or high side)transistors of the half bridges of the power stage. In this case, theseapparatus are sensitive to the intrinsic mismatch of the embedded senseelements.

SUMMARY

One embodiment of the present disclosure provides an apparatus fordetecting the rotor position of an electric motor which is lesssensitive to the supply variation.

Also, in the case of embedded sense elements, the apparatus according tothe present disclosure is less sensitive to the intrinsic mismatch ofthe embedded sense elements.

One embodiment of the present disclosure is an apparatus for detectingthe position of a rotor of a DC motor with N phases having a pluralityof windings, the apparatus comprising circuitry to couple at least twoof the windings between the supply voltage and ground according to afirst current path and allow the current stored in the two windings tobe discharged through a second current path, wherein the circuitry isconfigured to force the at least two windings at a short circuitcondition in the second current path. The apparatus also includes ameasurement circuit configured to measure the time period of dischargeof the current stored in the two windings, and a rotor position detectorfor detecting the rotor position based on the measured time period.

Another embodiment of the present disclosure is to provide an apparatusfor detecting the rotor position of an electric motor which is differentfrom prior art. Particularly, an apparatus for detecting the rotorposition of an electric motor according to the present disclosure mayreduce the current peak sunk from the power supply.

Another embodiment of the present disclosure is an apparatus fordetecting the position of a rotor of a DC motor with N phases having aplurality of windings, the apparatus comprising circuitry having atleast two half bridges coupled between the supply voltage and thereference voltage and having the central points coupled with the twowinding. The circuitry being configured to control a charge operation ofthe current passing through at least two of the windings and to controlthe discharge operation of the current stored in said two windings. Thecircuitry is also configured to drive the two half bridges in a pulsewidth modulation modality during the current charge operation and/orduring the current discharge operation. The apparatus includes ameasurement circuit configured to measure the time period of the currentcharge operation and/or the current discharge operation, and a rotorposition detector for detecting the rotor position based on the measuredtime period.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments thereof are now described, purely by way of non-limitingexamples and with reference to the annexed drawings, wherein:

FIG. 1 shows the partial diagram of a driving circuit of a brushlessmotor with an apparatus for detecting the position of the rotor of thebrushless motor according to an embodiment of the present disclosure;

FIG. 2 shows the current path of the current through the windings of thebrushless motor under a voltage pulse;

FIG. 3 shows the current discharge path of the current stored in thewindings of the brushless motor;

FIG. 4 is a time diagram of the current circulating through a load witha nominal supply voltage;

FIG. 5 is a time diagram of the current circulating through a load witha supply voltage increased and showing sense element has a unitary gain;

FIG. 6 is a time diagram of the current circulating through a load wherethe time period TON is decreased;

FIG. 7 is a time diagram of the current circulating through a load wherethe time period TON is greater than TOFF;

FIG. 8 is a time diagram of the current circulating through a loadshowing that the current does not depend on the supply voltage while thetime period TON decreases;

FIG. 9 is a time diagram of the current circulating through a loadshowing a decrease in both time periods TOFF and TON;

FIG. 10 shows a schematic diagram of a driving circuit of a brushlessmotor with an apparatus for detecting the position of the rotor of thebrushless motor according to another embodiment of the presentdisclosure;

FIG. 11a shows the waveforms of the power supply current and the currentpassing through the electric motor using a known inductive sense;

FIG. 11b shows the waveforms of the power supply current and the currentpassing through the electric motor using the apparatus in FIG. 10 orFIG. 1 during the charge step of the current passing through theelectric motor;

FIG. 12a shows the waveforms of the current passing through the electricmotor using a known inductive sense; and

FIG. 12b shows the waveforms of the current passing through the electricmotor using the apparatus in FIG. 10 or FIG. 1 during the discharge stepof current passing through the electric motor.

DETAILED DESCRIPTION

FIG. 1 shows an apparatus for detecting the position of a rotor of anelectric motor, in particular, a brushless motor SM according to a firstembodiment of the present disclosure. The electric motor is of theN-phase type, preferably having three phases.

The apparatus includes half-bridges S1, S2 and S3 for controlling thebrushless motor SM that includes a rotor. FIG. 1 shows the stator of theelectric motor SM with the three star-connected phases A, B and C. Eachof the half-bridges includes a high side transistor and a low sidetransistor, each one with the associated recirculating diode, indicatedrespectively by MHA, MLA and DHA, DLA for the half-bridge S1, and MHB,MLB and DHB, DLB for the half-bridge S2 and MHC, MLC and DHC, DLC forthe half-bridge S3. The high-side transistors have their drain terminalscoupled to the positive power supply voltage Vcc while the low-sidetransistors have the source terminals coupled to a reference voltage,for example ground GND, by means of respective sense elements senseA,senseB, senseC. The sense element may be a resistance, a Hall sensor orpreferably an embedded sense element, i.e., the MOSFET transistor whichis formed during the manufacturing of the low side transistors MLA, MLBand MLC. The sense elements senseA, senseB, senseC may have differentgains for the mismatch due to the manufacturing. The source terminal ofeach high-side transistor is coupled to the drain of each low-sidetransistor. The connection point of the half-bridge S1 corresponds tothe phase A and is coupled to a terminal of the winding LA. Theconnection point of the half-bridge S2 corresponds to the phase B and iscoupled to a terminal of the winding LB. The connection point of thehalf-bridge S3 corresponds to the phase C and is coupled to a terminalof winding LC. The other terminals of the windings LA, LB and LC arecoupled to one another. These windings diagrammatically depict a 3-phasespindle motor SM.

The gate terminals GHA, GLA, GHB, GLB, GHC, GLC of the transistors ofthe half-bridges S1-S3 are controlled by a control device MP, preferablya microprocessor, which permits to suitably power the phases A, B and Cof the motor SM. The voltages of back electromotive force (or BEMF) areat the terminals of the windings A, B and C. However, during themeasurement of the rotor position, the motor is stopped and BEMF=0, thatis the control device MP provides to stop the motor SM to measure theposition of the rotor.

The apparatus comprises a current measurement circuit comprising amultiplexer AMUX controlled by a signal SEL and adapted to select one ofthe sense currents deriving from the sense elements senseA, senseB,senseC and to send the selected sense current I to the non-invertinginput of a comparator COMP adapted to compare the sense current I with athreshold current k×Ith deriving from a digital-to-analogue converterDAC supplied by the digital data deriving from the microprocessor MP.

In operation, the supply voltage Vcc may change, that is the supplyvoltage may maintain at a level not constant for all the operation timeof the driving apparatus of the electric motor.

According to the present disclosure, when the electric motor SM isstopped and BEMF=0, a current pulse is applied to the load comprisingtwo or all the windings LA, LB and LC of the electric motor SM,preferably the series of two windings or the series/parallel arrangementof all the windings. A load comprising two windings may be formed bycoupling one winding with the supply voltage Vcc by turning on acorrespondent high side transistor of one half bridge, another windingto the reference voltage (ground) by turning on a correspondent low sidetransistor of another half bridge while the third winding is floating(at high impedance condition). A load including all the windings may beformed by coupling two windings with the supply voltage Vcc by turningon the correspondent high side transistors of the half bridges while thethird winding is coupled to the reference voltage (ground) by turning ona correspondent low side transistor of the third half bridge or bycoupling two windings with the ground by turning on the correspondentlow side transistors of the half bridges while the third winding iscoupled to the supply voltage by turning on the correspondent low sidetransistor of the third half bridge.

The application of the current pulse to the load formed by the motorwindings provides information depending on the load by allowing theprecise and reliable estimation of the rotor position. In fact theposition of the rotor is capable to modify the inductive value of thewindings which is due to the magnetic saturation. The position of therotor may be detected by analyzing the response of a current pulseapplied to one or more motor windings.

The apparatus for detecting the position of a rotor of an electric motoraccording to the present disclosure comprises the control device,preferably a microprocessor MP, to apply a current pulse to the motorwinding during the excitation step or charging step. Preferably themicroprocessor MP controls the turning on of one high side transistor ofone of the half-bridge S1-S3 and one low side transistor of a differenthalf-bridge S1-S3, for example by turning on the transistors MHA andMLB. In this way the current flows through the windings LA and LBaccording to a first current path PATH1 (FIG. 2).

The discharge step is obtained by forcing the windings LA and LB at ashort circuit condition and this occurs by turning on both thetransistors MLA and MLB using the microprocessor MP or turning on onlythe transistor MLB and forcing a high impedance condition of the halfbridge S1 (FIG. 3). In this way the discharge current I flows throughthe windings LA and LB according to a second current path PATH2. In thisway a single sense element for detecting the current in the first andthe second current paths is used. The sense element of the current inthe first and the second current paths is the sense element senseB.

The discharge current I(t)=I0×e^(−t/Tau) where I0 is the current valueat the beginning of the discharge step, Tau is the time constant of theload comprising the series of the windings LA and LB, therefore Taudepends on the features of the windings LA and LB. The value of I0 isthe peak value of the current in the first current path.

By calculating the time period TOFF needing the current I(t) to reachthe value k×I0, where K has a value lower than 1, the time period TOFFdepends on the winding features and not on the supply voltage or thevalue of I0. By fixing the current threshold Ith as the current peak I0,the value K×Ith is the value of the current I that determines the finalinstant of the time period TOFF. The peak value I0=Ith is the currentvalue when the discharging time period starts, that is the maximum valuereached by the current I in the second current path.

The apparatus comprises a measurement circuit configured to measure thedischarge time period TOFF of the current in the two windings LA and LBand a rotor position detector for detecting the rotor position based onthe measured time period TOFF. The measurement circuit and the rotorposition detector can be implemented by the microprocessor MP and by thecomparator COMP which is configured to compare the sensed current I withthe current threshold K×Ith (during the discharging time period TOFF orthe second current path PATH2).

As the excited phases change, the sense elements involved during thecurrent discharge step change. There is a need for the selector SEL toallow the comparator COMP to be coupled to the correct terminal. Inparticular, during the excitation of phase A-B, the multiplexer AMUXshould couple the comparator COMP to the sense element senseB; duringthe excitation of phase A-C, the multiplexer AMUX should couple thecomparator COMP to the sense element senseC; during the excitation ofphase B-C, the multiplexer AMUX should couple the comparator COMP to thesense element senseC; during the excitation of phase B-A, themultiplexer AMUX should couple the comparator COMP to the sense elementsenseA; during the excitation of phase C-A, the multiplexer AMUX shouldcouple the comparator COMP to the sense element senseA; and during theexcitation of phase C-B, the multiplexer AMUX should couple thecomparator COMP to the sense element senseB.

Preferably the determination of the rotor position is based on that thewinding impedance depends on the rotor position. For this reason and inparticular for a motor having three phases A, B and C, current I issequentially passed through the following pairs of phases A-B, A-C, B-C,B-A, C-A, C-B, and the time period TOFF is measured, for each pair ofphases, and the control circuit MP performs the suitable calculationsfor determining the rotor position.

FIG. 4 shows a time diagram of the current I circulating through a loadformed by two windings LA and LB when a current pulse Ip is applied tothe load with a supply voltage Vcc at the nominal value, for exampleVcc=5V, and wherein the sense element senseB has a unitary gain. Thediagram shows the charging step of the current I until reaching thecurrent threshold Ith and a discharging step of the current I untilreaching 50% of the current threshold Ith. The discharging step isobtained turning on both the transistors MLA and MLB by themicroprocessor MP while TON and TOFF are the time periods employed bythe current I to reach the current threshold Ith and 50% of the currentthreshold Ith. In this case it occurs TON=TOFF=97 microseconds.

FIG. 5 shows a time diagram of the current I circulating through a loadformed by two windings LA and LB when a current pulse Ip is applied tothe load with a supply voltage Vcc which has been increased with respectto the previous case of 20%. That is Vcc=6V, and wherein the senseelement senseB has a unitary gain. In this case the time period TON (75microseconds) is decreased with respect to the previous case in FIG. 4and the time period TOFF (97 microseconds) is unchanged. That is thetime period TOFF which measures the discharge time period of the currentI does not depend on the supply voltage Vcc.

FIG. 6 shows a time diagram of the current I circulating through a loadformed by two windings LA and LB when a current pulse Ip is applied tothe load with a supply voltage Vcc which has been increased with respectthe previous case of 20%, that is Vcc=6V, and wherein even the gain ofthe sense element senseB has been increased with respect the previouscase of 20%. In this case, the time period TON (59 microseconds) isdecreased with respect to the previous case in FIG. 5 and the timeperiod TOFF (97 microseconds) is unchanged, that is the time period TOFFwhich measures the discharge time period of the current I does notdepend on the supply voltage Vcc and the gain of the sense element.

FIG. 7 shows a time diagram of the current I circulating through a loadformed by two windings LA and LB when a current pulse Ip is applied tothe load with a supply voltage Vcc at the nominal value, for exampleVcc=5V, and wherein the sense element senseB has a unitary gain. Thediagram shows the charging step of the current I until reaching thecurrent threshold Ith and a discharging step of the current I untilreaching 50% of the current threshold Ith. The discharging step isobtained by turning on only the transistor MLB and forcing a highimpedance condition of the half bridge S1 while TON and TOFF are thetime periods employed by the current I to reach the current thresholdIth and 50% of the current threshold Ith. In this case it occurs thatTON (97 microseconds) is greater than TOFF (78 microseconds).

By increasing the supply voltage Vcc by 20% with respect the previouscase in FIG. 7, that is Vcc=6V (FIG. 8), the time period TOFF (78microseconds) remains unchanged. That is the time period TOFF whichmeasures the discharge time period of the current I does not depend onthe supply voltage Vcc while the time period TON (75 microseconds)decreases.

By increasing the gain of the sense element senseB by 20% with respectthe previous case in FIG. 8, that is Vcc=6 V and the gain of senseB is1.2 (FIG. 9), the time period TOFF (74 microseconds) and the time periodTON (59 microseconds) decrease.

Preferably the apparatus of an embodiment of the present disclosure isused for detecting the position of the rotor when the motor SM isstopped.

FIG. 10 shows an apparatus for detecting the position of a rotor of a DCmotor, in particular a brushless motor SM, according to anotherembodiment of the present disclosure. The electric motor is of theN-phase type, preferably having three phases.

The apparatus comprising the power stage includes the half-bridges S1,S2 and S3 for controlling the brushless motor SM having a rotor. FIG. 10shows the stator of the electric motor SM with the three star-connectedphases A, B and C. Each of the half-bridges consists of a high sidetransistor and a low side transistor, each with the associatedrecirculating diode, indicated respectively by MHA, MLA and DHA, DLA forthe half-bridge S1, and MHB, MLB and DHB, DLB for the half-bridge S2 andMHC, MLC and DHC, DLC for the half-bridge S3. The high-side transistorshave their drain terminal coupled to the supply voltage Vcc, derivingfrom a power supply 500 through a RC filter consisting of the resistanceRline and the capacitor Cf. The resistance Rline represents theresistance of the electric path between the power supply 500 and the PCBcomprising the power stages S1-S2 and the control unit. The capacitor Cfrepresents the capacitors coupled with the same PCB. The low-sidetransistors have the source terminal coupled to a reference voltage, forexample the ground GND, by means of respective sense elements senseA,senseB, senseC. The sense element may be a resistance, a Hall sensor orpreferably a MOSFET transistor, i.e. the MOSFET transistor which isformed during the manufacturing of the low side transistors MLA, MLB andMLC. The sense elements senseA, senseB, senseC may have different gainsfor the mismatch due to the manufacturing. The source terminal of eachhigh-side transistor is coupled to the drain of each low-sidetransistor. The connection point of the half-bridge S1 corresponds tothe phase A and is coupled to a terminal OUTA of the winding LA. Theconnection point of the half-bridge S2 corresponds to the phase B and iscoupled to a terminal OUTB of the winding LB, and the connection pointof the half-bridge S3 corresponds to the phase C and is coupled to aterminal OUTC of winding LC. The other terminals of the windings LA, LBand LC are coupled to one another. These windings diagrammaticallydepict a 3-phase spindle motor SM.

The gate terminals GHA, GLA, GHB, GLB, GHC, GLC of the transistors ofthe half-bridges S1-S3 are controlled by a control device MP, preferablya microprocessor, to suitably power the phases A, B and C of the motorSM.

The apparatus includes a current measurement circuit having amultiplexer AMUX1 controlled by a signal SEL1 and adapted to select oneof the sense currents deriving from the sense elements senseA, senseB,senseC, and a multiplexer AMUX2 controlled by a signal SEL2, and adaptedto select one of the terminals OUTA, OUTB, OUTC. The signals SEL1 andSEL2 are provided by the microprocessor MP.

The apparatus may also include a comparator CompTr where the positiveinput terminal of which is coupled to the output of the multiplexerAMUX1 and at a negative input terminal of which a threshold voltage Ithris applied, which derives from an digital to analog converter DACadapted to convert a digital signal deriving from the microprocessor MPinto the threshold voltage Ithr. The output OutTr of comparator CompTris coupled to the microprocessor MP.

The apparatus can include, alternatively or in addition to thecomparator CompTr, a comparator CompTf where the positive input terminalof which is coupled to the output terminal of the multiplexer AMUX2while the negative input terminal is coupled to the power supply voltageVcc. The output OutTf of comparator CompTf is coupled to the controlcircuit MP.

The apparatus shown in FIG. 10 uses the sense elements senseA, senseB,senseC for measuring the current circulating in the windings during theexcitation step, i.e. for calculating the rise time Tr, while it usesthe voltage drop at the terminals of the current recirculating diodes,coupled in parallel to the transistors of the half-bridges S1-S3, formeasuring the discharge or fall time Tf. However, other methods formeasuring the time periods Tr and Tf are applicable so that theapparatus in the FIG. 10 is therefore to be considered merelyindicative.

In accordance with the second embodiment of the present disclosure, theapparatus for detecting the position of the rotor is based on theanalysis of the current in the windings upon a PWM signal applied to thepower stage S1, S2, S3 during inductive sense. The determination of therotor position is based on that the winding impedance depends on therotor position, Preferably for a motor having three phases A, B and C,current Iload is sequentially passed through the following pairs ofphases A-B, A-C, B-C, B-A, C-A, C-B. The excitation of each one of thecouple of phases A-B, A-C, B-C, B-A, C-A, C-B occurs by way of the PWMpower stage with a duty-cycle lower than 100% during inductive sense.Therefore, by analyzing the current, i.e. by analyzing the rise time Tror the fall time Tf of the current Iload through two winding of theelectric motor SM upon the application of the PWM signal, the positionof the rotor may be determined.

With the power stage in PWM modality during the charging step of thecurrent in the motor windings, a lowering of the current peak sunk fromthe power supply occurs. In this way it is possible to use currents witha higher value than in the inductive sense methods previously known.Also the filtering effect of the RC filter formed by the resistor Rlineand the capacitor Cf has positive results in the case wherein the powerstage S1-S3 operates in PVM modality with a duty-cycle lower than 100%.

FIGS. 11a and 11b show the waveforms of the power supply current Ilineand the current Iload passing through the electric motor SM using aninductive sense, wherein the power stage is driven in full saturationduring charging step of the current in the motor windings (FIG. 11a ).Using the apparatus according to the second embodiment of the presentdisclosure, the power stage is driven in PWM with a duty-cycle of 50%during the charging step of the current in the motor windings (FIG. 11b). It is illustrated that the current peak of the power supply currentIline is lower in FIG. 11b than in FIG. 11 a.

With the power stage in PWM modality only during the discharge timeperiod of the current in the motor windings, a modulation of the currentdischarge time period is permitted.

Considering patent application US 2012/0098474, the specification ofwhich is incorporated in the present disclosure, for determining therotor position, the time period Ttot is measured, for each pair ofphases, where Ttot=Tr+Tf and the control circuit MP performs thesuitable calculations for determining the rotor position. According tothe method of the second embodiment of the present disclosure, thecharging step is obtained by applying the power supply voltage Vcc tothe pair of windings involved, e.g. windings LA and LB, while thedischarging step is obtained by applying a PWM driving signal to thepower stage S1 and S2 coupled to the pair of windings (e.g. LA and LBagain) during current discharge. In this way the duty-cycle of the PWMsignal can be modulated for obtaining Tr=Tf. That is the application ofthe PWM signal during the current discharge allows equalizing the timeperiod Tr and Tf.

FIGS. 12a and 12b show the waveforms of the current Iload passingthrough the electric motor SM using an inductive sense wherein the powerstage is driven in high impedance during the discharging step of thecurrent in the motor windings (FIG. 12a ). Using the apparatus accordingto the second embodiment of the present disclosure, the power stage isdriven in PWM during the discharging step of the current in the motorwindings (FIG. 12b ). FIGS. 12a and 12b illustrate that with theapplication of the PWM driving signal to the power stage during thedischarging step of the current Iload, that Tr=Tf is obtained bysuitable modulating of the duty-cycle of the PWM driving signal.

Preferably the determination of the rotor position is based on that thewinding impedance depends on the rotor position. For this reason, and inparticular for a motor having three phases A, B and C, current I issequentially passed through the following pairs of phases A-B, A-C, B-C,B-A, C-A, C-B, and the time periods Tr and/or Tf are measured, for eachpair of phases, and the control circuit MP performs the suitablecalculations for determining the rotor position.

The apparatus of the second embodiment of the present disclosure can beused for detecting the position of the rotor when the motor SM isstopped.

In accordance with the second embodiment of the present disclosure, eventhe apparatus for detecting the position of the rotor in FIG. 1 can beused by applying a PWM signal to the power stage S1, S2, S3 duringinductive sense and analyzing the current in the windings. In this case,the PWM signal is applied only during the charging step of the currentin the motor windings and when the motor SM is stopped.

1-21. (canceled)
 22. An apparatus for detecting a position of a rotor ofan electric motor having a plurality of windings, the apparatuscomprising: a circuit having at least two half-bridges coupled between asupply voltage and a reference voltage, the at least two half-bridgeshaving central points coupled with two windings of the plurality ofwindings; the circuit configured to control a current charge operationof a current passing through the two windings and to control a currentdischarge operation of the current stored in the two windings; thecircuit configured to drive the at least two half-bridges in a pulsewidth modulation mode during the current charge operation, the currentdischarge operation, or any combination thereof; a measurement circuitconfigured to measure a time period of the current charge operation, thecurrent discharge operation, or any combination thereof; and a rotorposition detector configured to detect the rotor position based on themeasured time period.
 23. The apparatus according to claim 22, whereinthe circuit is configured to drive the two half-bridges in a pulse widthmodulation mode with a duty-cycle lower than 100%.
 24. The apparatusaccording to claim 22, wherein the circuit is configured to stop theelectric motor to detect the rotor position.
 25. The apparatus accordingto claim 22, wherein the electric motor has three phases and threewindings, and the circuit is configured to control the current dischargeoperation of the current stored in the two windings for each pair ofphases of the electric motor.
 26. An apparatus for detecting a positionof a rotor of an electric motor having a plurality of windings, theapparatus comprising: a circuit comprising at least two half-bridgeshaving central points coupled with two windings of the plurality ofwindings and configured to control a current charge operation of acurrent passing through the two windings, control a current dischargeoperation of the current stored in the two windings, and drive the atleast two half-bridges in a pulse width modulation mode during at leastone of the current charge operation and the current discharge operation;a measurement circuit configured to measure a time period of at leastone of the current charge operation and the current discharge operation;and a rotor position detector configured to detect the rotor positionbased on the measured time period.
 27. The apparatus according to claim26, wherein the circuit is configured to drive the two half-bridges in apulse width modulation mode with a duty-cycle lower than 100%.
 28. Theapparatus according to claim 26, wherein the circuit is configured tostop the electric motor to detect the rotor position.
 29. The apparatusaccording to claim 26, wherein the electric motor has three phases andthree windings, and the circuit is configured to control the currentdischarge operation of the current stored in the two windings for eachpair of phases of the electric motor.
 30. A method for detecting a rotorposition of an electric motor having a plurality of windings by using acircuit comprising at least two half bridges coupled between a supplyvoltage and a reference voltage and having central points coupled withtwo windings of the plurality of windings, the method comprising:charging a current passing through two of the plurality of windings;discharging a current stored in the two windings; driving the twohalf-bridges in a pulse width modulation mode during the charging, thedischarging, or any combination thereof; measuring a time period of thecharging, the discharging, or any combination thereof; and detecting arotor position based on the measured time period.
 31. The methodaccording to claim 30, wherein a duty-cycle is lower than 100% for thedriving two half bridges in the pulse width modulation mode.
 32. Themethod according to claim 30, wherein a duty-cycle is 50% for thedriving two half bridges in the pulse width modulation modality.
 33. Themethod according to claim 30, further comprising: repeating the chargingand discharging for each one of pairs of phases of the electric motor;measuring the time period of each charging, discharging, or anycombination thereof; and detecting the rotor position based on themeasured time periods.
 34. A method for detecting a rotor position of anelectric motor having a plurality of windings by using a circuitcomprising at least two half bridges coupled between a supply voltageand a reference voltage and having central points coupled with twowindings of the plurality of windings, the method comprising: charging acurrent passing through two of the plurality of windings; discharging acurrent stored in the two windings; driving the two half-bridges in apulse width modulation mode during at least one of the charging and thedischarging; measuring a time period of at least one of the charging anddischarging; and detecting a rotor position based on the measured timeperiod.
 35. The method according to claim 34, wherein a duty-cycle islower than 100% for the driving two half bridges in the pulse widthmodulation mode.
 36. The method according to claim 34, wherein aduty-cycle is 50% for the driving two half bridges in the pulse widthmodulation modality.
 37. The method according to claim 34, furthercomprising: repeating the charging and discharging for each one of pairsof phases of the electric motor; measuring the time period of eachcharging, and discharging; and detecting the rotor position based on themeasured time periods.